Experimental Study on the Influence of Formation Lateral Pressure Coefficient on the Mechanical Properties of Double-Layer Lining Structure in Shield Tunnel

Nowadays, the construction scale of shield tunnels is getting bigger and bigger, and the strata crossed by the tunnel body are complicated and changeable, so it is often difficult to meet the requirements of tunnel safety and durability with single-layer tube lining structure, and thus the double-layer lining structure has been more widely concerned. In order to explore the applicability of double-layer lining structure of shield tunnel in different strata, relying on the Shiziyang Tunnel Project on the Guangzhou-Shenzhen High-Speed Railway, the change rule of the mechanical properties of double-layer lining structure under different strata conditions is comparatively analyzed with the coefficient of lateral pressure (0.5, 0.6, 0.7, 0.8) as an index through similar model experiment. The test results show that: the stratum lateral pressure coefficient increases, the double-layer lining as a whole tends to be more hydrostatic pressure field state, pipe lining and secondary lining limit axial force value increases, elasticity and plasticity critical point and the lagging of the internal force mutation point. When the lateral pressure coefficient increases from 0.5 to 0.8, the ultimate bearing capacity of double-layer lining increases by 66.39%, the maximum radial displacement decreases from 15.17mm to 9.45mm, the lateral displacement of pipe sheet lining is limited, and the secondary lining assists in the improvement of bearing capacity of pipe sheet lining. The degree of crack development of pipe sheet lining under high stratum lateral pressure condition decreased, the phenomenon of localized falling block was reduced, and the reliability of the overall structure of double-layer lining was improved.